Internal oxygen levels decrease during the growing season and with increasing stem height

Eklund, Leif

doi:10.1007/pl00009761

Cited by 40 publications

(22 citation statements)

References 5 publications

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“…These concentrations had only minor and reversible effects on parenchyma cells and it is concluded that low oxygen concentrations are unlikely to be the cause of heartwood formation. However, Spicer and Holbrook (2005) measured sapwood oxygen at only two times of the year, Eklund (2000) found values <1% of air in drought-stressed spruce trees, and sapwood cell death may only occur in times of stress with extremely low oxygen concentrations, which only long-term measurements are likely to detect.…”

Section: Discussionmentioning

confidence: 96%

“…In other species lacking such intercellular spaces, the cambium plus bark appear to be quite impermeable to gases and the transpiration stream is supposed to be the main source of oxygen for the xylem ). More recently, direct measurement of oxygen in the stem support this idea (Eklund 2000;del Hierro et al 2002;Mancuso and Marras 2003;Gansert 2003), though in times of zero sapflow, such as during the night and on wet and cool days, only the oxygen either diffusing radially or present in gas spaces or dissolved in water is available.…”

Section: Introductionmentioning

confidence: 88%

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Gas diffusion through wood: implications for oxygen supply

Sorz

Hietz

2005

Trees

146

127

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Living tissue in tree stems has to be supplied with oxygen, which can be transported upwards with the transpiration stream; but in times of zero sapflow, the only source is the oxygen stored or diffusing radially through bark and xylem. We measured radial and axial diffusion of oxygen against nitrogen gas in wood of coniferous (Picea abies (L.) Karst. and Taxus baccata L.), ring-porous (Quercus robur L. and Fraxinus excelsior L.) and diffuse-porous (Fagus sylvatica L. and Carpinus betulus L.) trees at different water and gas contents in the laboratory. The diffusion coefficient (D) in radial direction was mostly between 10 −11 and 10 −7 m 2 s −1 and was strongly related to the gas content. At 40% gas volume, D increased 5-13-fold in Picea, Taxus and Quercus, 36-fold in Fraxinus, and about 1000-fold in Carpinus and Fagus relative to D at 15% gas volume. In the axial direction, diffusion was 1 or 2 orders of magnitude faster. Between-species differences in diffusion velocities can largely be explained by wood structure. In general, D was lowest in conifers, highest in diffuseporous and intermediate in ring-porous hardwoods, where the large vessels were mostly blocked by tyloses. Model calculations showed that at very high water content, radial diffusion can be too low to ensure the supply of respiring sapwood with sufficient oxygen and an important function of gas in living stems appears to be the supply of oxygen through storage and diffusion.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 88%

Gas diffusion through wood: implications for oxygen supply

Sorz

Hietz

2005

Trees

146

127

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“…A similar dependence may exist for stem tissues. Temporal and spatial variation in the concentration of oxygen within the stem (Eklund 2000) may also affect the rate of respiration (Sorz and Hietz 2006) and, hence, the variability in the relationship of R S to temperature.…”

Section: Xylem Co 2 Concentrationsmentioning

confidence: 99%

Stem respiration and carbon dioxide efflux of young Populus deltoides trees in relation to temperature and xylem carbon dioxide concentration

et al. 2007

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Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO(2) to the atmosphere (E (A)), commonly used to estimate the rate of respiration (R (S)), and stem temperature (T (st)) have often been poorly correlated, which we hypothesized was due to transport of respired CO(2) in xylem sap, especially under high rates of sap flow (f (s)). To test this, we measured E (A), T (st), f (s) and xylem sap CO(2) concentrations ([CO(2)*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated R (S) by mass balance as the sum of both outward and internal CO(2) fluxes and hypothesized that R (S) would correlate better with T (st) than E (A). We found that E (A) sometimes correlated well with T (st), but not on sunny mornings and afternoons or on rainy days. When the temperature effect on E (A) was accounted for, a clear positive relationship between E (A) and xylem [CO(2)*] was found. [CO(2)*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO(2)*] were related to changes in f (s) but not T (st). We conclude that changes in both respiration and internal CO(2) transport altered E (A). The dominant component flux of R (S) was E (A). However, on a 24-h basis, the internal transport flux represented 9-18% and 3-7% of R (S) on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on E (A) measurements. Unexpectedly, the relationship between R (S) and T (st) was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.

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“…A more reasonable assumption is that the water O 2 was equilibrated in the roots, and hence was close to equilibration with the stem O 2 and can take up even smaller amounts of O 2 . Some studies have suggested that the transpiration stream can provide O 2 to the sapwood (Eklund, 2000;Gansert, 2003). However, given the low solubility of O 2 in respect to respiration rates (as discussed above), this flux of O 2 is small, and thus can be important only in areas where respiration rates are extremely low and atmospheric O 2 diffusion is restricted.…”

Section: Explaining the Measured Arq Valuesmentioning

confidence: 99%

Internal respiration of Amazon tree stems greatly exceeds external CO<sub>2</sub> efflux

et al. 2012

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Abstract. Respiration in tree stems is an important component of forest carbon balance. The rate of CO 2 efflux from the stem has often been assumed to be a measure of stem respiration. However, recent work in temperate forests has demonstrated that stem CO 2 efflux can either overestimate or underestimate respiration rate because of emission or removal of CO 2 by transport in xylem water. Here, we studied gas exchange from stems of tropical forest trees using a new approach to better understand respiration in an ecosystem that plays a key role in the global carbon cycle. Our main questions were (1) is internal CO 2 transport important in tropical trees, and, if so, (2) does this transport result in net release of CO 2 respired in the roots at the stem, or does it cause the opposite effect of net removal of stem-respired CO 2 ? To answer these questions, we measured the ratio of stem CO 2 efflux to O 2 influx. This ratio, defined here as apparent respiratory quotient (ARQ), is expected to equal 1.0 if carbohydrates are the substrate for respiration, and the net transport of CO 2 in the xylem water is negligible. Using a stem chamber approach to quantifying ARQ, we found values of 0.66 ± 0.18. These low ARQ values indicate that a large portion of respired CO 2 (∼ 35 %) is not emitted locally, and is probably transported upward in the stem. ARQ values of 0.21 ± 0.10 were found for the steady-state gas concentration within the stem, sampled by in-stem equilibration probes. These lower values may result from the proximity to the xylem water stream. In contrast, we found ARQ values of 1.00 ± 0.13 for soil respiration. Our results indicate the existence of a considerable internal flux of CO 2 in the stems of tropical trees. If the transported CO 2 is used in the canopy as a substrate for photosynthesis, it could account for up to 10 % of the C fixed by the tree, and perhaps serve as a mechanism that buffers the response of the tree to changing CO 2 levels. Our results also indicate, in agreement with previous work, that the widely used CO 2 efflux approach for determining stem respiration is unreliable. We demonstrate here a field applicable approach for measuring the O 2 uptake rate, which we suggest to be a more appropriate method to estimate stem respiration rates.

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Internal oxygen levels decrease during the growing season and with increasing stem height

Cited by 40 publications

References 5 publications

Gas diffusion through wood: implications for oxygen supply

Gas diffusion through wood: implications for oxygen supply

Stem respiration and carbon dioxide efflux of young Populus deltoides trees in relation to temperature and xylem carbon dioxide concentration

Internal respiration of Amazon tree stems greatly exceeds external CO<sub>2</sub> efflux

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Internal oxygen levels decrease during the growing season and with increasing stem height

Cited by 40 publications

References 5 publications

Gas diffusion through wood: implications for oxygen supply

Gas diffusion through wood: implications for oxygen supply

Stem respiration and carbon dioxide efflux of young Populus deltoides trees in relation to temperature and xylem carbon dioxide concentration

Internal respiration of Amazon tree stems greatly exceeds external CO&lt;sub&gt;2&lt;/sub&gt; efflux

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Internal respiration of Amazon tree stems greatly exceeds external CO<sub>2</sub> efflux